It is conventional, as part of the manufacturing process, after integrated circuits have been sealed in plastic packages to subject the devices to selected tests prior to shipment to enable differentiation between satisfactory and unsatisfactory products. Input and output characteristics of the IC chips, pulse characteristics, noise leeway and the like, are tested in an electrical property test. Those IC devices that pass the electrical property test are then subjected to a burn-in test in which the devices are arranged in an oven and caused to perform for a selected period of time under a power source voltage which is approximately 20 per cent higher than their rated value and at an elevated temperature, for example, 120.degree. C. Those IC devices that fail to perform satisfactorily in the burn-in test are discarded as being unsatisfactorily and only those products which continue performing normally are shipped out as satisfactory.
An electronic integrated circuit package, known as a ball grid array (BGA) package, in which ball-shaped terminal leads (solder balls) are arranged in a selected matrix on the bottom side of the package, has become popular in recent years as a new surface loading type of IC package. The BGA package has an advantage in that the pitch of the terminals can be increased and the terminal leads are sturdier and more difficult to deform by contact with other members.
FIGS. 11 through 15 show conventional sockets used for burn-in tests of such BGA packages. As shown in FIG. 11, socket 101 has a resinous base 102 in the shape of a rectangle on which a slider 104 is movably mounted in a horizontal direction, i.e., parallel to the y arrow of FIG. 11, for loading a BGA package 105 (FIG. 15(a)). Slider 104 has a recessed holding part 104a (FIGS. 15(a)-15(c)) with an aperture corresponding to each lead terminal 105b of BGA package 105 formed in its bottom wall. In addition, a contact maker 106 is fixed to base 102 and extends through each aperture. Contact makers 106 are elongated metallic members each having a pair of arms 106a and 106b (FIG. 11 (a)) provided at one end thereof. Each contact maker 106 is vertically fixed on base 102, with arms 106a and 106b facing upwardly.
A cover 103 made of resin and having a centrally disposed opening 103a is movably mounted on base 102 in the vertical direction relative to the base and biased upwardly by a compression coil spring 136 provided at each of four corners. A slide mechanism is provided on both sides of slider 104 for moving the slider in parallel with the bottom wall of base 102. A generally L-shaped arm 107 is rotatably mounted at one end of base 102 at 108 and is rotatably linked to a shaft 109 that engages with an end portion of slider 104. One end of a lever 110 is rotatably mounted on shaft 111 as the center at an opposed end portion of base 102. The tip end part of arm 107 is movably connected to lever 110 through a slot located intermediate the ends of the lever by means of a pin 112. The distal end tip part of the arm 110 engages the margin of the wall defining the opening in cover 103 when cover 103 is in its raised position. Moreover, compression coil springs 113 (FIG. 11) are provided on the shaft 111 side of the slider to place a bias on slider 104 in the y direction as seen in FIG. 11.
When cover 103 is pushed down from the position shown in FIG. 15(a) to the FIG. 15(b) position, lever 110 rotates toward base 102 and slider 104 moves in the direction indicated by arrow H in conformity with the movement of the arm 107 and shaft 109. As a result, arms 106a and 106b of contact makers 106 are pushed by grid or lattice parts 104c to open (FIG. 11(a)). If a BGA package 105 is dropped into holding part 104a of slider 104 in this state, as shown in FIG. 15(b), terminal leads 105a of BGA package 105 enter the respective gaps between arms 106a and 106b. When the downward force against cover 103 is removed, lever 110 and arm 107 rise as shown in FIG. 15(c), with slider 104 being returned in a direction which is opposite to the direction indicated by arrow H, with a result that arms 106a and 106b of each contact maker 106 are closed and that each terminal lead 105b of BGA package is held by arms 106a and 106b of a respective contact maker 106. As a result of this, each terminal lead 105b of BGA package can be electrically connected to a respective contact maker 106 in a satisfactory manner. BGA package 105 can be easily removed from the socket by pressing the cover downwardly.
A socket according to prior art as described, nevertheless, has the following problems: The use of the link mechanism comprising lever 110 and arm 107, employed as a means for moving the slider 104, results in an increased number of parts as well as an increase in manufacturing cost and results in a more complicated assembling operation. Further, because slider 104 moves in a direction parallel to the bottom wall of base 102, it is necessary to provide space for movement of slider 104 between open and closed positions of contact makers 106 and this has prevented the pitch between the contact makers 106 from being reduced. Those BGA packages 105 which have little space between terminal leads 105b present a problem in that respective terminal leads 105a tend to enter the gap between the arms of two different contact makers 106 upon being loaded in the socket with a result that it becomes difficult for BGA package 105 to be inserted. In addition, since the electrical connection is effected by sandwiching the terminal leads 105a of the BGA package, there have been cases where terminal leads 105b have fused to contact makers 106 at the time of a burn-in test, thereby making it difficult for the BGA package 105b to be taken out.